A device as specified in the opening paragraph is known from United States Patent U.S. Pat. No. 4,289,513, in which the filter element consists, for example, of a corrugated sheet of fibrous sorption paper which is impregnated with a finely particulate active substance, such as activated carbon or activated silica gel. When air is caused to flow through such a filter element (e.g. in an air intake filter for an internal combustion engine), gaseous pollutants, such as fuel vapors, are intended to be filtered out mainly via a physical reaction with the active substance.
A disadvantage of such a filter element is that it is relatively ineffective in filtering out gaseous pollutants having a molecular weight below about 50-60 (and thus possessing a high volatility). This is inter alia due to the fact that absorption of such volatile substances by activated carbon, alumina or silica gel occurs via a rather weak physical interaction, together with the fact that the activity of such substances is rather "general" in nature, in that they cannot be efficiently targeted at specific gaseous pollutants. In addition, the absorption of many gaseous pollutants by activated carbon, alumina or silica gel deteriorates at high relative humidities (RH.gtoreq. about 60%). As a result, many gaseous substances will only be partially filtered out by the known filter, whereas other gaseous substances (such as NH.sub.3 and formaldehyde vapor, for example) will not be removed at all.